Electric fuse including heater winding for solder joint



April 11, 1967 F. J. KOZACKA ELECTRIC FUSE INCLUDING HEATER WINDING FOR SOLDER JOINT Filed 001;. 19, 1965 FIG. 2

FIG. I

FIG. 3

INVENTOR FREDERICK J. BY M/vww W KOZACKA ATTORNEY 3,313,899 ELECTRIC FUSE INCLUDING HEATER WINDING FOR SOLDER JOINT Frederick J. Kozaeka, South Hampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Oct. 19, 1965, Ser. No. 498,027 2 Claims. (Cl. 200-123) This invention relates to electric fuses, and more particularly to electric fuses including a spring-biased solder joint for interrupting protracted small overload currents and further including a fusible element for interrupting major fault currents, or short-circuit currents, wherein the solder-joint and the fusible major fault current interrupting element are connected in series with a heater element, Such fuses require the presence of an electric heater element for heating the solder joint 'by the same current which flows through the solder joint and the fusi- 'ble element for interrupting major fault currents.

The design of the heater element is primarily determined by the time current curve required of the fuse to protect a given piece of equipment as, for instance, a given electric motor. Hence there is a relatively limited freedom in regard to selection of the parameters of the heater element, its parameter being largely determined by the thermal characteristics of the piece of equipment which the fuse is supposed to protect. In a like fashion the parameters of the fusible element responsive to major fault currents are primarily dictated by the characteristics of the piece of equipment to be protected by the fuse, and hence there is very little freedom in regard to the selection of the parameters of that fusible element.

If the heater and the fusible element for major fault current protection are both determined according to the performance characteristics. imposed upon the fuse by the equipment to be protected by it, there is a likelihood that the i -r value for thermal destruction of the heater and the i -t value for thermal destruction of the fusible element responsive to major fault currents will be relatively close. This then results in an almost simultaneous vaporization of the heater element and of the fusible element responsive to major fault currents. Assuming that the i -t value required for thermal destruction of the heater element is larger than the fusing i 't value of the fusible element responsive to major fault currents, but less than the normal clearing or total i -t value of the fusible element responsive to major fault currents; in such an instance an arc will be kindled at the gap formed by thermal destruction of the heater, and the vapors evolved by that arc will contaminate the arc gap resulting from fusion and vaporization of the fusible element responsive to major fault currents. These vapors have generally a relatively low ionizing potential and, therefore, their presence is adverse to a rapid and effective interruption of the faulted circuit by the fuse. The presence of such low ionizing potential vapors is particularly detrimental in fuse structures wherein the springbiased solder joint and the fusible element responsive to major fault currents are both air immersed for reasons of design simplicity, i.e. in fuses wherein for reasons of economy the presence of a pulverulent arc-quenching medium is disposed with.

It is, therefore, an object of this invention to provide electric fuses of the aforementioned type which are not subject to the above limitations and drawbacks.

It is another object of this invention to provide electric fuses of the aforementioned type whose performance is not adversely affected by thermal destruction of the heater element thereof occurring incident to a major fault current, or short-circuit current.

Still another object of this invention is to provide elec- United States Patent "ice tric fuses of the aforementioned type having an air immersed spring-biased solder joint and an air immersed fusible element responsive to major fault currents-as distinguished from devices including a pulverulent arcquenching filler-whose interrupting capacity is not seriously impaired by an accidental thermal destruction of the heater for the solder joint.

Further objects and advantages of the invention will become apparent as this description proceeds, and the features of novelty of the invention will be pointed out with particularity in the claims annexed to, and forming part of, this specification.

For a better understanding of the invention reference may be had to the accompanying drawings wherein' FIG. 1 is mainly a longitudinal section of a fuse embodying this invention with the parts thereof in operative positions, some of these parts being shown in front elevation rather than in section;

FIG. 2 is a view of the same structure as FIG. 1, shown in the same fashion as in FIG. 1, and showing the constituent parts of the fuse upon fusion of the solder joint and interruption of the circuit as a result of a protracted small overload current; and

'FIG. 3 is a section along 3-3 of FIG. 1.

Referring now to the drawings, numeral 1 has been applied to indicate a substantially tubular casing of insulating material closed on both ends thereof by terminal elements 2 in the form of metal caps, or metal ferrules. Reference numeral 3 has been applied to indieate a support member of insulating material arranged in coaxial relation to, and inside of, casing 1 and supporting on the axially inner end thereof a metallic contact element 4 having a substantially V-shaped slot or recess 5. Support member 3 supports a resistance heater ele ment formed by a helically wound wire 6. The axially outer end of wire 6 extends through an aperture in one of caps 2 into a pool 7 of solidified solder contained in a recess defined by the aforementioned cap 2. The other end of resistance Wire 6 engages the V-shaped slot or recess 5 in contact element 4. Reference numeral 8 has been applied to indicate a fusible element responsive to major fault currents, but not affected by protracted relatively small overload currents. Fusible element 8 is preferably formed by a metal ribbon having a plurality of serially arranged perforations defining a plurality of serially arranged points of reduced cross-section. In instances where the circuit voltage of the circuit in which the fuse is to be used is relatively small and where the current-carrying capacity required of the fuse is likewise relatively small, fusible element 8 may be formed by a relatively thin wire of uniform cross-section. The axially inner end of fusible element 8 is bent to V-shape and inserted into the V-shaped slot or recess 5 of contact element 4 and firmly held therein against the bias of a helical spring 10 by a mass of solder 9. The axially outer end of spring 10 is bent around one of the rims of casing 1 and firmly held in position by the action of one of the caps 2. This cap 2 defines a recess filled with a mass 7 of solder establishing a conductive connection between the axially outer end of fusible element 8 and the cap 2. The axially inner end of spring 10 is attached in any desired fashion to the axially inner end of fusible element 8. Wire 6 forming the heater for solder joint 9 is enveloped by a helically wound woven sleeve of glass cloth, and fusible element 8 is likewise enveloped by such a sleeve of glass cloth to which refer ence numeral 12 has been applied.

On occurrence of protracted relatively small overloads solder joint 9 is caused to melt on account of the heat generated in heater wire 6. As a result, spring 10 pulls the axially inner end of fusible element 8 out of engagement with solder joint 9 and contact element 4, thus forming a relatively long circuit-interrupting break, as clearly shown in FIG. 2. a

On occurrence of major fault currents, or short circuit currents, fusible element 8 and heater wire 6 may fuse and vaporize in rapid sequence, or virtually simultaneously, and thus the vapors resulting from vaporization of the heater wire will have a tendency to contaminate the arc gap formed by vaporization of fusible element 8. This is, however, effectively avoided 'by the provision of sleeve 11 which condenses a portion of the metal vapors resulting from vaporization of heater wire 6, and thus tends to preclude such vapors from reaching the arc gaptresulting from vaporization of fusible element 8. Glass cloth sleeve 12 forms, so to speak, a second line of defense against access of products of arcing resulting from vaporization of heater wire 6 to the arc gap space taking the place of fusible element 8. In addition thereto glass cloth sleeve 12 condenses metal vapors resulting from vaporization of fusible element 8, and to such extent performs the duty of a pulverulent arcquenching filler with which many fuses are provided. It will, however, be observed that the structure shown in the drawing does not lend itself to the provision of a pulverulent arc-quenching filler since the presence of such a filler would preclude the separation of the axially inner end of fusible element 8 from solder joint 9 and from contact element 4 as illustrated in FIG. 2. Glass cloth sleeve 12 is so flexible as not to impair the rapid separation of the axially inner end of fusible element 8 from solder joint 9 and from contact element 4.

Although this invention has been described in considerable detail, it is to be understood that such description of the invention is intended to be illustrative rather than limiting, as the invention may be variously embodied, and is to be interpreted as claimed.

I claim as my invention:

1. An electric fuse comprising in combination:

(a) a substantially tubular casing of insulating material;

(b) a pair of terminal elements closing the ends of said casing;

(c) means for conductively interconnecting said pair of'terrninal elements, said interconnecting means including a heater element wound of resistance wire, a fusible element responsive to major fault currents connected in series with said heater element, and, a spring-biased solder joint heated by said heater element, said solder joint being interposed between one end of said heater element and said fusible element responsive to major fault currents having relatively close i -t values resulting in a likelihood of substantially simultaneous vaporization of said heater element and of said fusible element responsive to major fault currents on occurrence of such fault currents; and

(d) a sleeve of woven glass cloth surrounding said resistance wire of said heater element for controlling the vapors resulting from vaporization of said heater element.

2. An electric fuse comprising in combination:

(a) a substantially tubular casing of insulating material;

(b) a pair of terminal elements closing the ends of said casing;

(0) air immersed current interrupting means conductively interconnecting said pair of terminal elements, said current interrupting means including a heater element wound helically of resistance wire,

a fusible element responsive to major fault currents connected in series with said heater element, and a' spring-biased solder joint heated by said heater element, said solder joint being interposed between one end of said heater element and said fusible element responsive to major fault currents having relatively close i -t values resulting in a likelihood of substantially simultaneous vaporization of said heater element and said fusible element responsive to major fault currents on occurrence of such fault currents;

(d) a first sleeve of woven glass cloth enveloping said fusible element responsive to major fault currents; and

(e) a second sleeve of woven glass cloth said second sleeve being wound helically and enveloping said resistance wire of said heater element.

References flited by the Examiner UNITED STATES PATENTS 699,647 5/ 1902 Black 200-123 2,111,749 3/ 1938 Bussrnann 200123 2,113,155 4/1938 Kiefer 200 -123 2,833,890 5/1938 Jacobs 20013l 2,856,488 10/1958 Kozacka 200- 3,144,534 8/1964 Baumbach 200l23 H. B.. GILSON, Assistant Examiner.

BERNARD A. GILHEANY, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,313,899 April 11, 1967 Frederick J. Kozacka It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 63, for "dispensed" read disposed column 4, lines 1 and 25, after "currents", each occurrence,

insert said heater element and said fusible element responsive to major fault currents Signed and sealed this 14th day of November 1967.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer i Commissioner of Patents 

1. AN ELECTRIC FUSE COMPRISING IN COMBINATION: (A) A SUBSTANTIALLY TUBULAR CASING OF INSULATING MATERIAL; (B) A PAIR OF TERMINAL ELEMENTS CLOSING THE ENDS OF SAID CASING; (C) MEANS FOR CONDUCTIVELY INTERCONNECTING SAID PAIR OF TERMINAL ELEMENTS, SAID INTERCONNECTING MEANS INCLUDING A HEATER ELEMENT WOUND OF RESISTANCE WIRE, A FUSIBLE ELEMENT RESPONSIVE TO MAJOR FAULT CURRENTS CONNECTED IN SERIES WITH SAID HEATER ELEMENT, AND, A SPRING-BIASED SOLDER JOINT HEATED BY SAID HEATER ELEMENT, SAID SOLDER JOINT BEING INTERPOSED BETWEEN ONE END OF SAID HEATER ELEMENT AND SAID FUSIBLE ELE- 